Many people have covered the basic lessons on how to deploy VDI, so this article offers some uncommon knowledge -- hands-on intelligence that one can only acquire on the bumpy road.

Use cases can be blurry. Don’t expect users to fall neatly into persistent and non-persistent categories. We found that desktops we treated and perceived as non-persistent in the physical world actually have elements of persistence. But we discovered even deeper fuzziness than anticipated. We have “faculty” users, for example, who are not a homogenous group. Some faculty members moved to VDI and are perfectly happy with it. Others we’re not even trying to move because they do a lot of research with large data sets, and we’re not sure that a virtual desktop can handle the resource requirements.

There are always outliers. Still other users proved unsuitable for VDI for small but critical reasons. One faculty member was accustomed to plugging in 5 or 6 USB devices, which would sometimes freeze or crash the virtual desktop. Another faculty member runs a lot of DVDs but the virtual desktop wouldn't recognize the DVD player on her “thick” client (traditional PC running a virtual desktop) because it wasn’t a USB device, and a USB player attached to a thin client produced really choppy results.

Video? It depends. With VDI, there’s also the concern over video and how well it displays. As described above, physical DVDs don’t work well, but streaming video can be just fine. We’ve found it works great with PCoIP, and not very well using RDP as the brokering protocol.

Antivirus software – enough said. It’s fairly common knowledge that traditional antivirus software doesn’t always work well in a virtual environment. We put a new antivirus program that was not optimized for virtual workloads and found it slowed desktops to a grinding halt. Conclusion: get antivirus that is optimized for virtual desktops or can be reconfigured to run well in a virtual environment.

Different setup, different experiences. There are also inherent differences between physical and virtual desktops that require some differences in setup, and sometimes result in different end-user experiences. A non-persistent virtual desktop, for example, is truly non-persistent – every time you reboot the machine you have to run through the new Word/Excel/PPT setup processes (you know, where it asks for your initials?), and if you run Firefox, you have to click through the “do you want this to be your default browser” windows. This can be a little frustrating for users, and requires you to use GPOs or some other method to address these items, if you don’t want users to have the “Groundhog Day” experience each and every time they use a virtual desktop. Not so with an imaged computer, where you can run through these things and then “freeze” the computer. (This is also now the case with virtual desktops created by Unidesk, which is a huge help.) This speaks a bit to the idea that a non-persistent computer really isn’t fully non-persistent – in many cases we actually require some small amounts of persistence for settings, printers, and so on.

A need for speed, at what cost? Depending on your server, network, and storage infrastructure, as well as how you’re configuring your desktops (memory, processors), there may be speed or performance differences between physical and virtual desktops. In cases where we have an entire room or lab of machines, no one has complained about (or possibly even noticed) a performance issue – the user experience is fine. But some of our employees, who are in the process of transitioning over to VDI as their primary computer, seem to more easily notice a slight speed/latency/lag difference with virtuals that didn’t exist with their physical machine. This lag can be exacerbated if the user is the sort that likes to keep a lot of windows open. We believe that there is—and that we have achieved—an “acceptable” performance level and user experience, but each organization will need to determine for themselves what this is, and work with users to recognize that it may be different, but not necessarily bad. Beefier servers and faster storage can improve performance, but you need to be able to invest in the infrastructure.